CHICAGO (Reuters) - Failure to approve the Trans-Pacific Partnership trade deal would be a major setback for U.S. interests in Asia as Washington seeks to deepen alliances in the region, Secretary of State John Kerry said on Wednesday, urging Congress to ratify the pact.

The 12-nation Pan-Pacific trade deal championed by President Barack Obama has been pilloried by both major-party nominees in the U.S. presidential race, Democrat Hilary Clinton and Republican Donald Trump.

While Republicans have traditionally backed free trade deals, Trump has blamed them for U.S. job losses and threatened to rip them up or renegotiate them if he wins the Nov. 8 election.

“If we see the TPP rejected, it would be a gigantic self-inflicted wound – a setback to our own interests in the region,” Kerry told the Chicago Council on Global Affairs, in remarks that drew a smattering of applause and boos.

“It would amount to a conscious turning of our backs on the Asia Pacific at the very moment that we ought to be linking arms – it would be an act that will hurt American workers, slow our economy, hinder our ability to advance the full range of U.S. objectives” in the fast-growing region, he added.

Republican leaders have said there is no point in bringing the trade deal for a vote in the “lame-duck” session of Congress after the election.

But Kerry urged Congress to approve the deal after the election, saying: “It’s the right thing to do for America – and no matter what the loudest voices may be shouting – it is also the popular choice.”

There are concerns in Washington that failure to pass the TPP would prompt Southeast Asian nations to turn to China and Russia.

Kerry said the trade deal was a “litmus” test of Washington’s capacity to lead and was necessary if the United States wanted a steady and reliable presence in the region.

His comments came amid tensions with China over the disputed South China Sea, increased concerns over North Korea’s missile and nuclear weapons programs, and questions over the future of the U.S.-Philippines alliance.